1. Field of the Invention
The present invention relates to elastic endless crawlers or tracks for earth-moving machines, agricultural equipment and the like, in which the track is assembled over drive wheels.
2. Description of the Prior Art
Vehicles such as earth-moving machines and agricultural equipment are constructed with endless tracks which are driven by drive wheels. The track or belt is assembled over a plurality of wheels, at least one of which is a drive wheel, and is engaged by the drive wheel. Increasingly, vehicles used in agriculture are driven by track systems because the tracks have higher traction in soil and cause less ground compaction than vehicles equipped with conventional, pneumatic tires. As a result of this renewed interest in track systems, many improvements in such systems have recently been implemented.
One such improvement, set forth in U.S. Pat. No. 5,279,378 sets forth a vehicle having an endless belt with a highly tensioned elastomeric exterior surface which provides improved frictional coupling between its interior surface and the drive wheel. The improvement is directed to belt tensioning aspects of the invention. The improvement discloses an endless belt comprised of at least one reinforcing filament wrapped substantially parallel to the longitudinal axis of the chassis.
Other improvements, such as described in U.S. Pat. Nos. 5,295,741, 4,678,244 and 4,057,302 are directed at improving the coupling between the interior surface of the track and the drive wheel of the vehicle. While many belts or tracks utilize rubber lugs to accomplish the coupling, such as set forth in U.S. Pat. No. 5,279,378, these improvements utilize core bars, typically of a material of a different composition than the rubber track, to improve coupling.
While some of these improvements are effective, the methods for manufacturing reinforced, endless rubber track for propulsion of agricultural or earth-moving vehicles is both expensive and time-consuming.
Some methods and apparatus are available for making V-belts which may also be applicable to tractor treads or belts. The description of such apparatus and methods is set forth in U.S. Pat. Nos. 2,867,845 and 4,861,403. However, because of the large differences in the sizes of V-belts, which are small, typically having widths measured in inches and fractions thereof, compared to the rubber track utilized in earth-moving vehicles, typically having widths measured in feet, simple scale up of V-belt technology may not always be practical and may not yield usable rubber track because of the size differences.
U.S. Pat. No. 2,867,845 depicts apparatus and method for forming a continuous V-belt. The V-belt is formed in segments and has lugs formed on one side. While such a method and apparatus are suitable for forming continuous V-belts, there are problems with applying these methods to the manufacture of the large tracks required for agricultural or earth-moving equipment. When the V-belts are manufactured in segments and vulcanized in the molds, the segments have parting lines therebetween which are undesirable. Because the segments are individually formed, with each segment vulcanized, the rubber between the segments is not vulcanized across the parting lines, resulting in a discontinuous region. This discontinuous region has less strength than the surrounding vulcanized, cross-linked region. If the tracks are not vulcanized in the mold during forming, but rather formed as green rubber belts and vulcanized separately after forming, then another time-consuming operation is required to vulcanize the rubber after the green belt is formed. Furthermore, since the green rubber belt is vulcanized after molding, the rubber belt no longer being contained by the mold during heating and pressurization, the likelihood of distortion and melting of the belt as a result of out-of-tolerance conditions is significantly increased.
U.S. Pat. No. 4,861,403 is similar to the method of U.S. Pat. No. 2,867,845, but differs in that a fabric-reinforced double toothed belt is formed. As one side of the belt is formed with teeth, it is partially vulcanized. In a subsequent operation, the second side of the belt is formed with teeth, and then the entire belt is vulcanized.
The present invention is directed to an improved rubber track made in accordance with an improved method and with improved-apparatus, overcoming the deficiencies and short-comings of the prior art methods and apparatus for producing endless track.